This invention generally relates to the field of intravascular balloon catheters, and more particularly to a balloon catheter with a radiopaque balloon.
Percutaneous transluminal coronary angioplasty (PTCA) is a widely used procedure for the treatment of coronary heart disease. In this procedure, a balloon dilatation catheter is advanced into the patient""s coronary artery and the balloon on the catheter is inflated within the stenotic region of the patient""s artery to open up the arterial passageway and thereby increase the blood flow there through.
To facilitate the advancement of the dilatation catheter into the patient""s coronary artery, a guiding catheter having a preshaped distal tip is first percutaneously introduced into the cardiovascular system of a patient, using the Seldinger technique, through the brachial or femoral arteries. The catheter is advanced until the preshaped distal tip of the guiding catheter is disposed within the aorta adjacent the ostium of the desired coronary artery. The distal tip of the guiding catheter is then maneuvered into the ostium. A balloon dilatation catheter may then be advanced through the guiding catheter into the patient""s coronary artery until the balloon on the catheter is disposed within the stenotic region of the patient""s artery. The balloon is inflated to open up the arterial passageway and increase the blood flow through the artery.
The physician uses fluoroscopy to observe the balloon and properly place it within the stenosis. The catheter shaft generally has radiopaque markers on its inner member within the balloon, so the placement of the balloon can be determined before inflation. In spite of this, the precise location of the balloon frequently cannot be reliably determined by using the radiopaque markers alone.
After placement, the operator will inject radiopaque materials, such as Renograffin, into the inflation lumen to inflate the balloon. The radiopaque material allows the operator to view the inflation of the balloon. However, such radiopaque materials are expensive, and the viscosity is high so that inflation and deflation times are slow compared to saline solution.
Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not over expand to the point of damaging the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In a large number of angioplasty procedures, there may be a restenosis, i.e. reformation of the arterial plaque. To reduce the restenosis rate and to strengthen the dilated area, physicians now frequently implant an intravascular prosthesis called a stent inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent is left in place within the artery at the site of the dilated lesion. See for example, U.S. Pat. No. 5,507,768 (Lau et al.) and U.S. Pat. No. 5,458,615 (Klemm et al.), which are incorporated herein by reference.
However, extremely flexible balloons lack support when the balloon is maneuvered through a stenosis. First, the balloon has a tendency to bend easily in the transition areas, which are the areas proximal and distal to the stent placement. Second, the balloon may fold back on itself in the transition areas when force is applied longitudinally to attempt to cross a stenosis. Both cases cause reduced access and cross ability, making proper placement within the stenosis more difficult.
If the balloon is not properly placed during a dilatation, and especially during a stenting procedure, the inflation of the balloon and stent against the vessel wall may cause damage to the non-stenosed tissue. Proper placement is difficult because the balloon itself is not generally radiopaque, so the operator does not have the precise location of the balloon, the working length and the stent. Radiopaque markers on the inner member of the catheter shaft aid in stent placement but the location of the markers are not a guarantee of the location of the balloon and the stent within the stenosis.
Therefore, what has been needed is a balloon catheter with improved radiopaque properties to improve placement and visibility of the balloon. Additionally, a balloon catheter with improved stiffness, especially in the transition areas, has also been needed to improve cross ability. The present invention satisfies these and other needs.
The present invention is directed to a balloon for an intracorporeal catheter with at least a portion of its walls having radiopaque properties. The balloon is formed of a polymeric material, which has a deflated single wall thickness of at least 0.001 inches to about 0.0125 inches, preferably about 0.005 inches to about 0.012 inches.
The thickness of the balloon wall allows for a substantial amount of radiopaque material to be doped into the walls, creating a truly radiopaque balloon. In thinner wall balloons, adding enough radiopaque material to make the balloon easily visible will change the properties of the balloon. The radiopaque layer is about 0.00025 inches to about 0.012 inches for sufficient radiopacity without changing the properties of the balloon. Specifically, the radiopaque layer is about 0.002 inches to about 0.003 inches. The thick walls additionally allow for addition of other materials to enhance any properties of the balloon.
The balloon is formed of a polymer material. Specifically, polymers creating balloons having a thicker wall when deflated, and a thinner wall when inflated, are available for this invention. These types of balloons are known as formed in place balloons because they are generally formed during dilatation at the desired location, as opposed being pre-formed, then wrapped about the catheter shaft before entry and unwrapped upon dilatation.
More specifically, the balloon is preferably formed of porous expanded polytetrafluoroethylene. Examples of porous expanded polytetrafluoroethylene are described in U.S. Pat. No. 3,953,566 (Gore), U.S. Pat. No. 4,187,390 (Gore) and U.S. Pat. No. 5,753,358 (Korleski), all assigned to W. L. Gore and Associates, Inc., which are incorporated herein by reference. An additional preferred polymer material is ultra high molecular weight polyethylene. However, any polymer that creates a balloon having walls with a deflated minimum thickness of 0.001 inches would be suitable for the radiopaque balloon of this invention.
The present invention is also preferably constructed with layers to allow control over the eventual radiopaque properties of the finished balloon. Balloons can be constructed in layers by many methods known in the art. These methods include, but are not limited to, wrapping the balloon material about a mandrel, dipping a mandrel into a polymeric dispersion, and sputtering the polymeric dispersion on to a mandrel. The method using layers gives control over the process so that the radiopaque material can be either layered or combined with the balloon material in specific designs and at specific locations.
The radiopaque portion may be either doped into the polymeric material at a loading percentage of about 70% to about 90%, or deposited on the outer wall, the inner wall, or between layers of the balloon. The radiopaque material could be located on all or part of the balloon. The placement of the radiopaque material can make any shape on the balloon, including but not limited to diamonds, circles, rings and stripes. Any design, shape or placement of the radiopaque material is available because of the controlled manufacture. For both embodiments, the layer containing the radiopaque material is about 0.00025 inches to about 0.012 inches, preferably 0.002 inches to about 0.003 inches.
Another embodiment of the invention includes elastomeric or inelastic material combined within the balloon or as a layer adjacent to the balloon. Such embodiments could combine the properties of known balloons with the radiopaque properties available in this invention. Such properties include, but are not limited to, better inflation and deflation characteristics.